It's widely mentioned that Redis is "Blazing Fast" and mongoDB is fast too. But, I'm having trouble finding actual numbers comparing the results of the two. Given similar configurations, features and operations (and maybe showing how the factor changes with different configurations and operations), etc, is Redis 10x faster?, 2x faster?, 5x faster?

I'm ONLY speaking of performance. I understand that mongoDB is a different tool and has a richer feature set. This is not the "Is mongoDB better than Redis" debate. I'm asking, by what margin does Redis outperform mongoDB?

Take the results with a grain of salt of course! If you are programming in another language, using other clients/different implementations, etc your results will vary wildy. Not to mention your usage will be completely different! Your best bet is to benchmark them yourself, in precisely the manner you are intending to use them. As a corollary you'll probably figure out the best way to make use of each. Always benchmark for yourself!

It's worth commenting that MongoDB and Redis have different persistence structures, and that Redis only supports a data schema that is able to fit in memory. Though ram is cheap, if you need to use/store more than 12-16GB of data, I'd see what your server options look like.
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Tracker1Jul 25 '12 at 21:46

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@sivann this post goes from no benchmarks to a clearly stated "rough" benchmark. Don't be a troll with the "benchmarks are misleading" nonsense. Of course different conditions can alter the results. Contribute back and submit your own benchmarks that test your case and link from this post instead, then we'll all benefit from your "tested" opinion.
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Homer6Jan 7 '13 at 18:38

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@sivann The default (shipped) configuration is what this benchmark was testing. IMHO, the default configuration determines which side of the fsync fence a package sits on. For Redis, it's advertised as a memory server that urges people to use other alternatives when the database is larger than the total system memory. For MongoDB, it's advertised as a database. Postgres would never turn off fsync because they're clearly in the persistence camp. Most people don't modify the configurations, so this benchmark is somewhat accurate for those cases.
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Homer6Jan 8 '13 at 22:09

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I agree with @sivann, the benchmark you posted is fatally flawed. MongoDB is multi-threaded and Redis is not. If your benchmark was multi-threaded you would see that MongoDb actually has higher throughput on a multi-core machine.
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ColinMJan 17 '13 at 18:49

In my case, what has been a determining factor in performance comparison, is the MongoDb WriteConcern that is used. Most mongo drivers nowadays will set the default WriteConcern to ACKNOWLEDGED which means 'written to RAM' (Mongo2.6.3-WriteConcern), in that regards, it was very comparable to redis for most write operations.

But the reality is depending on your application needs and production environment setup, you may want to change this concern to WriteConcern.JOURNALED (written to oplog) or WriteConcern.FSYNCED (written to disk) or even written to replica sets (back-ups) if it is needed.

Then you may start seeing some performance decrease. Other important factors also include, how optimized your data access patterns are, index miss % (see mongostat) and indexes in general.

Here is an excellent article about session performance in the Tornado framework about 1 year old. It has a comparison between a few different implementations, of which Redis and MongoDB are included. The graph in the article states that Redis is behind MongoDB by about 10% in this specific use case.

Redis comes with a built in benchmark that will analyze the performance of the machine you are on. There is a ton of raw data from it at the Benchmark wiki for Redis. But you might have to look around a bit for Mongo. Like here, here, and some random polish numbers (but it gives you a starting point for running some MongoDB benchmarks yourself).

I believe the best solution to this problem is to perform the tests yourself in the types of situations you expect.

The Tornado benchmarks align well with my own tests in using Redis and MongoDb as a Zend_Cache backend. The richer functionality of MongoDb lets you use fewer requests and the multi-threaded design scales far better than a single Redis process which is not multi-threaded. Conclusion is that MongoDb scales higher. Also, Redis no longer supports virtual memory.
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ColinMJan 17 '13 at 18:56

Up to 5000 entries mongodb $push is faster even when compared to Redis RPUSH, then it becames incredibly slow, probably the mongodb array type has linear insertion time and so it becomes slower and slower. mongodb might gain a bit of performances by exposing a constant time insertion list type, but even with the linear time array type (which can guarantee constant time look-up) it has its applications for small sets of data.

Numbers are going to be hard to find as the two are not quite in the same space. The general answer is that Redis 10 - 30% faster when the data set fits within working memory of a single machine. Once that amount of data is exceeded, Redis fails. Mongo will slow down at an amount which depends on the type of load. For an insert only type of load one user recently reported a slowdown of 6 to 7 orders of magnitude (10,000 to 100,000 times) but that report also admitted that there were configuration issues, and that this was a very atypical working load. Normal read heavy loads anecdotally slow by about 10X when some of the data must be read from disk.